Hey Pearl,
Peel strength probably isn't going to help too much in this case. What you need to know is the ultimate tensile strength of the resin just below the land, at a temperature between Tg and solder alloy solidus.
The proposed metric for the resin itself is "fracture toughness". There is a draft method within IPC now. There is a proposal to add it to future revs of 4101. I think Microtek Labs has it implemented. One complication I suspect is that if the fractures consistently occur at the glass just below the land, then modeling the resin by itself may not be that helpful.
Have you investigated any possible changes in material, or maybe a switch to/from a foil lam build?
Chris
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of pearl petras
Sent: Thursday, February 04, 2010 10:47 AM
To: [log in to unmask]
Subject: Re: [TN] track lifting
More info
5 mil trace, 0.5oz Cu. Board is 10 layer, .063"
The material is rated to IPC4101B/129.
Still trying to find out the reflow profile.
The board sees double-sided reflow. Not sure if the BGA is on 1st or 2nd side.
There may also be a repetitive mechanical stress factor though, based on how the board is installed in the chassis.
Had occasional intermittents before, but now we have a few occurrences over a short period of time.
A peel strength test apparently passed, but that was done on the board after the 2 reflow cycles. Would that potentially influence the results if possibly the board material wasn't properly cured?
--- On Wed, 2/3/10, pearl petras <[log in to unmask]> wrote:
> From: pearl petras <[log in to unmask]>
> Subject: Re: [TN] track lifting
> To: [log in to unmask]
> Received: Wednesday, February 3, 2010, 10:26 AM
> I'll see what I can do to reply to
> all the questions.
> 676 ball, 1 mm pitch, 27mm sq
> tracks lifted on only one side of device.
> not all tracks lifted, and sometimes non-adjacent tracks
> lifted, which was a mystery to us, but if John is noticing
> some tracks are broken, that might explain it. We
> hadn't noticed that yet.
> leadfree
> Has happened a few times. We are trying to determine
> when in the process, now. Unsure if during production
> or only after it leaves our facility.
>
>
> Thanks for all the replies so far.
>
>
> --- On Wed, 2/3/10, Leland Woodall <[log in to unmask]>
> wrote:
>
> > From: Leland Woodall <[log in to unmask]>
> > Subject: Re: [TN] track lifting
> > To: [log in to unmask]
> > Received: Wednesday, February 3, 2010, 9:57 AM
> > Brian,
> >
> > Was the strain you mention below originate from the
> reflow
> > process? Was
> > it because of a thermal mismatch or an accelerated
> cooling
> > rate?
> >
> > Just curious...
> >
> > Leland
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]
> > On Behalf Of Brian Chandler
> > Sent: Wednesday, February 03, 2010 7:28 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] track lifting
> >
> > We just conducted a study on acceptable strain levels
> for
> > lead free
> > products.
> > Our BGA test coupons showed this exact result from
> excess
> > strain.
> >
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